We have previously demonstrated that may patients with Syndrome X (chest pain despite angiographically normal coronary arteries) have myocardial ischemia due to limited coronary flow reserve (microvascular angina). Because lidoflazine, a calcium entry blocker, improves chest pain symptoms and effort tolerance in patients with microvascular angina, we studied the effect of this drug on coronary hemodyanmics in 10 patients with microvascular angina. All had been significantly symptomatic on conventional calcium channel blockers and had improved symptomatically on lidoflazine 240-360 mg/d. Compared to measurement of coronary (great cardiac vein) flow off all medications, lidoflazine resulted in improved coronary flow response to pacing stress, even after administration of ergonovine 0.15mg. Further, coronary flow reserve following pharmacologic vasodilation by dipyridamole 0.75 mg/kg was also significantly improved. Thus, lidoflazine results in significant improvement in stress and pharmacologic coronary flow reserve, and suggests that coronary flow reserve in patients with microvascular angina is limited by vasoconstrictor influences related to abnormal calcium fluxes.